Directional boring apparatus for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled though the soil by means of a powerful hydraulic device such as a hydraulic cylinder or winch. A drill head for boring in soil, rock or both is disposed at the end of the drill string and may include an ejection nozzle for water or other drilling fluid to assist in boring. In other applications, tools such as reamers, pipe bursters, impactors, slitters and pullers are used to slit, burst and replace existing underground pipelines.
Ideally, drill heads and other tools in use in horizontal directional drilling and pipe replacement should be coupled to the drill string and/or other tools in a manner that permits rapid replacement. Tool breakage, changes in strata and similar circumstances often require on site tool changes and replacements. If it is desired to first forward drill a pilot hole and then pull a back reamer through the hole to widen it, it is necessary to uncouple the sonde housing (if used) and drill bit from the drill string in the exit pit and mount the back reamer in place of these components. Consequently, couplings or joints that enable rapid tool changes are very desirable.
Further, the mechanical stresses and abrasive conditions that horizontal drilling and underground pipe replacement tools undergo are severe. Joints between a drill string and tool are subjected to severe torque loadings and longitudinal stresses in these operations. These conditions tend to wear joints rapidly, requiring frequent replacement. Threaded connections are susceptible to thread wear and joint loosening. Failure of a joint in a horizontal drilling or pipe replacement operation can result in a tool stuck in a borehole or pipe, necessitating costly and time consuming excavation to recover the tool or form a bore around the location at which the tool was lost.